Optical, electronic and optoelectronic devices are currently being developed using Group III-V semiconductor materials. In particular, many of these devices are being developed on InP or InP-substrate based systems. Long wavelength, index guided, injection lasers are one example of devices formed on an InP substrate.
Fabrication techniques for making these devices including the index guided, injection lasers depend upon a knowledge of the substrate wafer orientation prior to such processing steps as photolithographic masking or etching, for example. In the case of the index guided laser, it is necessary to obtain the substrate wafer orientation in order to form either the mesa or channel which defines the optical waveguide of the laser.
Various techniques have been used to orient substrate wafers. In general, the prior techniques have incorporated a processing step which causes at least partial destruction of the working surface, i.e., the (100) surface, by either etching or masking. For example, T. Kambayashi et al. in Jap. J. of Appl. Phys., Vol. 19, No. 1, pp. 79-85 (1980), show an orientation technique wherein the working surface of a Group III-V semiconductor material substrate is chemically etched to produce geometrically definable etch pits such as long, narrow grooves or ellipsoids or the like at the sites of dislocations, defects or other imperfections in the surface of the crystalline structure. The etch pits are then examined to determine the relative orientation of an axis of each etch pit. One drawback of this technique is the requirement that the defects or imperfections exist in the crystalline structure so that the desired etch pits are produced when the material is chemically etched. Another exemplary orientation technique is shown by K. Iga et al. in IEEE J. of Quantum Electronics, Vol. QE-16, No. 10, pp. 1044-1047 (1980). In this technique, the working surface of the material is photo-lithographically masked with a cross-hatched pattern. Subsequently, unmasked portions of the working surface are contacted by a chemical etchant to reveal different sidewall geometries in the etch pits so made. The material is cleaved through the cross-hatched pattern in order to reveal different cross-sectional views on the (011) and (011) surfaces. Inspection of the sidewall geometries allows one to identify the (011) or (011) surfaces. However, this technique suffers from the drawback that photolithographic masking must be performed on the working surface of the material in order to orient the crystal. Furthermore, a portion of the working surface is destroyed in orienting the material.